1. Field of the Invention
The present invention relates to a car mounted navigation system.
2. Description of the Related Art
Generally, prior-art car mounted navigation systems store map data on a storage medium such as CD-ROM and displays the map data on the screen of a car mounted display in a car travel so as to indicate a current position and destination of a car on map images appearing on the display screen.
These car mounted navigation systems require the need for translating a map information into a database. In addition, since the prior-art car mounted navigation systems are self-contained and compare data produced by a car mounted distance sensor and azimuth sensor with map data in order to determine current positions of a car, they require accurate map data in order to achieve an error-free accurate navigation. Thus, it is critical to the prior-art car mounted navigation systems how many actual road geometries are accurately translated into a database.
The Geographical Survey Institute of Ministry of Construction takes a policy of correcting a 1/25,000 scale topographical national map providing a means for supporting the translation into the database once or more every 5 years. However, various land readjustments and road-makings or road-repairings quickly change geometries of roads, so that the national map cannot follow such changes to contain many regions which have not been corrected even for 10 years or more.
On the other hand, Japan Digital Road Map Association etc. are digitizing all of 2.5 m wide roads in Japan in order to translate data of the 2.5 m wide roads into a database. However, it seems that the digitization will much delay, a cost for maintaining the database of the roads will very high and the completion of the digitization will require a period of 6-10 years. In addition to the situations of the map database making, there is a problem in that the map database has many drawbacks so that the car mounted self-contained navigation system fails due to the inapplicability of road data of an area or a missing of road data.
In order to solve the problems, the applicant for the present inventors filed Japanese patent applications HEI. 1-65648 and HEI. 1-149357 both containing a car mounted navigation system which required no database-made map data. This navigation system picks up a course to be travelled of a car from a paper map and digitizes it into navigation data by means of a separate digitizer so as not to require a great amount of database-made map information. This car mounted navigation system has well eliminated the drawbacks in the prior-art car mounted self-contained navigation systems while yet requiring a data-making with the digitizer.